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Chapter 11 - Ceramics: Inorganic, non-metallic compounds formed by heat. Examples:

*See notes at bottom. Disk brake, silicone carbide. Ball Bearing: Silicone Nitride, Si 3 N 4 or Alumina Oxide or Zirconia. Porcelain high voltage insulator. Chapter 11 - Ceramics: Inorganic, non-metallic compounds formed by heat. Examples:. Rocket Nozzle: Silicone Nitride, Si 3 N 4.

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Chapter 11 - Ceramics: Inorganic, non-metallic compounds formed by heat. Examples:

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  1. *See notes at bottom Disk brake, silicone carbide Ball Bearing: Silicone Nitride, Si3N4 or Alumina Oxide or Zirconia Porcelain high voltage insulator Chapter 11 - Ceramics: Inorganic, non-metallic compounds formed by heat. Examples: Rocket Nozzle: Silicone Nitride, Si3N4 Ceramic inserts, cutting tools, tungsten carbide See HO for Common Types Knife: Zirconium dioxide, Dental implants ZrO2

  2. III. Types of Ceramics:

  3. I. Overview of ceramics: Characterized by: • Compounds between metallic and non-metallic elements (i.e. Si and O, Si and N, Al and O, etc..) • Frequently oxides, nitrides and carbides (i.e. silicon carbide – SpinWorks) • Can be crystalline or amorphous • Very strong covalent (sharing of electrons) or ionic (transfer of electrons) bonds. • Properties include: • Strong but brittle • Low fracture toughness • Good insulators of electricity BUT good conductor of heat (i.e. comparable to metals have reasonably high thermal conductivity, k) – this is unique to ceramics. • Excellent high temp properties • Low coef of thermal expansion

  4. I. Nature of ceramics: Example: Aluminum Oxide, Al2O3 Covalent = strong Electrons tied up

  5. II. Properties of Ceramics • Benefits: • High chemical resistance • High melting point and therefore high operating T. • Extremely hard and stiff (i.e. 180 E6 psi) • Good electrical insulator (electrons tied up). Exception = superconductors • Good thermal conductor (high K like metals) • But, low thermal expansion and good thermal stability • Good creep • High modulus • High compressive strength

  6. II. Properties of Ceramics • Shortcomings: • Low tensile strength and BRITTLE. Sut = Suc/10. Do not readily slip like metals but fracture. • Catastrophic failure • The bond is ionic and covalent. A material held by either type of bond will tend to fracture before any plastic deformation can occur! • Low fracture toughness (1/10 to 1/100 KIC compared to metals) • Materials tend to be porous and microscopic imperfections act as stress concentration decreasing the toughness further. • Elongation = 0% • Low fatigue strength • Large statistical spread and less predictable than metals (size, shape and location of internal flaws is likely to differ from part to part) • Prone to thermal shock • Hard to machine and form • Cost 8X more than metals • See Table 8.2

  7. Search area 1 2 Ranked by Index 3 Results 22 pass Material 1 2230 Material 2 2100 Material 3 1950 etc... Optimized selection using charts

  8. Electrical Resistance: Ceramics = good electrical insulators, but…

  9. Good conductors: metals and ceramics Good insulators: polymer foams, cork, wood, cardboard…. Selection: one-property indices Good thermal conductors!

  10. III. Types of Ceramics: (see HO 6 – 10): • Structural (clay) and whiteware: bricks, pipes, floor and roof tiles, dinner ware, chinca, etc… • Refractory ceramics: kiln lingings, high T capability most are based on silicates (sand) • Glass, amorphous ceramic, most based on silica, SiO2 • Annealed glass • Tempered glass • Laminated glass Go to HO pg 6!!

  11. III. Types of Ceramics: (see HO 6 – 10): d) Technical or engineering ceramics – 3 categories: • Oxides (alumina, zirconia) semiconductors • Non-oxide (carbides, borides, nitrides) i.e. tungsten carbide cutting tools, silicone nitride ball bearings, silicone carbide furnace inserts. • Cermits or composites – combination of metals and ceramics (powder metallurgy), combines high strength and hardness, thermal characteristic of ceramics with toughness of metals)

  12. V. How to Strengthen: (see HO 4,5): • Flame polishing to reduce surface cracks • Close surface cracks use in compression (or compress with metal band) • Atom gun to fill in surface cracks (fires ions into cracks) • Reduce crystal size • Laminate or anneal (glass) • Combine materials to increase toughness (cermits)

  13. V. Manufacturing – see HO • In situ – cement – mix powder with water • Sintering based methods WATCH!!!! http://www.youtube.com/watch?v=69Y0VuOYqkU http://ceramicinjectionmolding.com/

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